Will Rosetta find life on Churyumov-Gerasimenko 67P?

A small European spacecraft could take a giant leap in explaining the origins
of life on our planet

As you read this, hundreds of millions of miles away, a spacecraft the size of a fridge is preparing to separate from its mothership and float gently down to a frozen remnant of the birth of the solar system. It will be, if it works, an extraordinary achievement – one of humanity’s most impressive. If you want to get an idea of the scale, and the precision, of the European Space Agency’s Rosetta mission to the comet Churyumov-Gerasimenko 67P, imagine firing a shell from London and hitting the head of a nail in New Delhi.

The Rosetta spaceship has been shooting silently through space for 10 years. In that time it has travelled about 4 billion miles; for two years, it was shut down, to preserve energy, before being woken up in May. Two months ago, it reached its target, a lump of ice and soot about 2.5 miles across, and began, slowly, to circle it – the first man-made object to orbit a comet. Then it began to look for a suitable spot on the comet’s surface. And now, it is getting ready to launch a little object from within itself to land and dig into the surface, and to learn something more about the origins of the solar system, and of life itself.

The scientific possibilities are enormous – but the engineering challenges are equally so, says Dr Lewis Dartnell, an astrobiologist at the University of Leicester. First, Rosetta had to catch up with the comet – 67P is falling towards the Sun very quickly, about 84,000mph, he says, so you have to move very fast. To get up to that speed, Rosetta had to do two slingshot manoeuvres around Earth, and one around Mars – stealing a little bit of speed off each of them. As a result both planets are now moving imperceptibly slower than they were before Rosetta set off.

“But there was also the opposite problem,” says Dartnell. “Because the comet is so tiny, you can’t just slow down as you get to it using its own gravity as you can on a Mars mission. You need to travel at incredibly high speed to catch up to it and then slow down very precisely, using thrusters, to orbit it.”

But that sort of precision is tricky, for a very simple reason. Rosetta and its comet are, at the moment of writing, 315,890,887 miles from Earth; light takes nearly 30 minutes to reach it, so it is impossible to control the spacecraft remotely. Instead, the probe is doing everything itself. But that means that the mission’s controllers no longer have any real input into what happens. “It’s up to the spacecraft now,” says Dr Matt Taylor, the Rosetta mission’s project scientist. “We’ve done the best we can. It’s up to the lander, and gravity, and hopefully they’ll be kind.”

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Taylor is confident (“I have to be,” he says. “I’m the cheerleader for the mission”), but there are plenty of hurdles still to clear. A few moments after 9am British time tomorrow morning, Philae, as the lander is called, will separate from the main Rosetta spacecraft, and drift slowly – very slowly, slower than walking pace, taking seven hours to travel 14 miles – to the comet. “The gravity on the comet is one 10,000th that on Earth,” says Dartnell. “That’s a problem for Philae, because you don’t want it to bounce – it has to touch as gently as possible, and then fire a harpoon to attach itself on to the surface.”

Even then, things can go wrong. For two months, the Rosetta craft scanned the surface of the comet, and back home the team argued over where to land. “There’s always a big argument,” says Dartnell, a veteran of several Mars missions. “Do you pick the most scientifically interesting place, or the safest one?”

The two will probably be mutually exclusive: interesting will mean varied, while safe will mean uniform. “One of the landing sites looked perfect,” sighs Taylor, “but when you looked closer, it was strewn with thousands of 50-metre boulders.” In the end they chose a compromise site, which is now known as Agilkai, after an island in the mouth of the Nile.

If Philae survives the landing, though, it should start making some scientific breakthroughs. It may be small, but it is packed with instruments – a camera, a drill, a magnetic field detector, a ground-penetrating radar to see into the comet’s interior. “Why comets are so interesting is because they’ve been in deep freeze since the birth of the solar system,” says Dartnell. “By digging into it, Philae will be able to tell what temperature the comet was when it formed – which sounds boring, but immediately begins to tell us what the solar system was like in its very early years.”

One thing it will tell us about is the origin of life. Very few serious scientists believe that life was brought to Earth on a comet – that hypothesis, known as panspermia, is “crazy”, according to Dartnell. But a modified version of that theory is that the complex organic molecules from which life is made were carried here on a comet.

“From my point of view as an astrobiologist, this is the exciting bit. It’s the first time we’ll see pristine samples of comet from under the surface. So we’ll be looking at the degree of complexity of the molecules,” says Dartnell. “Will they just be simple volatile chemicals, ammonia and methane and methyl alcohol, or will there be more complicated things like amino acids and nucleic acids, the building blocks of protein and DNA?”

An impression of the Philae lander at work on Comet 67P/Churyumov-Gerasimenko more than 300 million miles away

If there are – or if there are even more complex things, chains of several amino acids, for instance – that could imply that such molecules were brought to Earth on a comet. If confirmed, that would be dramatic news. But not as dramatic as the alternative, which is that life is easier to make than we thought. For if carbon can form such complex molecules even in the cold of outer space, says Dartnell, then “almost certainly that chemistry was going on much quicker on the warm, wet Earth.”

And if life is easier to make than we thought, then it is more plausible that we might one day find it elsewhere. Already there is excitement. A chemical detector, a sort of robotic nose, on the Rosetta orbiter, has detected some organic chemicals in the cloud around the comet.

According to Taylor, it “smells like a stag do”: urine and alcohol and a sulphurous eggy smell. This is the stuff of life.

There is a tendency around huge, expensive projects like this to ask what practical benefits can come of it, as if new understandings of the universe are not enough on their own. But, says Dartnell, the benefits will be real. “Every time we send a probe we get better at it – we become a better space-faring species. We could use lots of the same technology for comet-mining or asteroid-mining, for human missions to Mars,” he says.

And there is the more basic benefit, that the technology required to make scientific instruments lightweight, small and energy-efficient enough to be useful in space also makes them more useful on Earth. One organic-molecule detector developed for the Beagle 2 Mars mission has been adapted as a breathalyser to detect disease in Africa.

First and foremost, though, this is a voyage of discovery. Philae will sit on the surface of 67P, recharging itself with its solar panels and sending back data until around March, when the great heat of the Sun will finally burn it out. Its parent Rosetta, meanwhile, will orbit the comet until the end of next year. Through them, humanity will be able to watch, for the first time, a comet drawing near our star, and, as it heats in the Sun’s rays, a great tail of gas and dust streaming off it. Then we will know a little bit more about the universe, and ourselves, than we did before.